We propose to determine the amount of gastrin by immunoassay procedures and the number and distribution of gastrin cells in the antrum, duodenum and pancreas obtained from young adult Wistar rats. These parameters will be correlated with the amount of gastrin released by these three tissues studied by in vitro perifusion procedures. A comparison will be made of the response of the three kinds of tissue to stimulatory and inhibitory factors known to affect gastrin release from antral tissue. Another objective is to achieve the cellular localization of a new polypeptide with gastrin-like activity which has been isolated from human, porcine, bovine and avian pancreas. The possible relationship of this pancreatic cell to the gastrin cell will be studied.